The present invention relates to the art of thermographic imagery and, in particular, an apparatus and method for improving thermographic imagery through the use of controlled temperatures.
The medical community became interested in thermography as a diagnostic tool as early as 1956, when it was discovered that skin overlying breast cancer had elevated temperatures as compared to normal tissue. Several thermographic systems have become available in the United States including the AGA THERMOVISION, BOFORS M-101, SPECTROTHERM AND THERMISCOPE. Contact thermograpy utilizing liquid crystals calibrated to change color at predetermined temperatures became available in 1969. Liquid crystal films embedded in elastomeric film became available in 1980.
Despite the great advances in imaging processes, designs and electronic hardware, thermography remains plagued with numerous false negatives and false positive results which detract from its usefulness as a diagnostic tool. The problem with present thermographic techniques is related to its dependence on passive measurements of surface temperature of the subject skin. Various surface temperature variations and the presence of nonspecific isotherms occur frequently. The surface temperature of the skin is a nonspecific physiological modality, heavily influenced vascular changes, changes in biological activity, tissue conductivity, and environmental factors.
In conventional thermography, objects with the same surface temperature will appear the same because they have the same isotherms. Objects with the same surface temperature as their surroundings cannot be distinguised or separated. In conventional thermography, a tumour is usually suspected on the basis of abnormal heat patterns due to increased vascularization or asymetry. However, conventional thermography is unable to reveal any pathological signs in a large number of patients with carcinomas due to the fact that as many as 30% of carcinomas may not produce any heat and are of the same temperature as the surrounding tissue.
Although it has been recognized previously that cooling, by evaporating alcohol from skin surfaces, and air conditioned rooms, may enhance thermographic images, such techniques do not provide precise regulation of temperature of the skin surface and underlying tissue to provide fine details. Although it has been recognized that cooling accentuates temperature differentials, the optimium cooling conditions have not been known. The use of cooling wraps were suspected of practical use, as evidenced by a paper entitled: "Temperature Measurements of Localized Pathological Processes" by R. N. Larson and J. P. Gaston, but have not been investigated substantially.